The invention is based on a fuel injection method and systems for an internal combustion engine as set forth hereinafter.
One such injection system has been disclosed by European Patent Disclosure EP 0 711 914 A1, for instance.
For the sake of better comprehension of the ensuing description, several terms will first be defined further: In a pressure-controlled fuel injection system, by means of the fuel pressure prevailing in the nozzle chamber of an injector, a valve body (such as a nozzle needle) is opened counter to the action of a closing force, and the injection opening is thus opened for an injection of the fuel. The pressure at which fuel emerges from the nozzle chamber into the cylinder is called the injection pressure. Within the scope of the invention, the term stroke-controlled fuel injection system is understood to mean that the opening and closure of the injection opening of an injector are accomplished with the aid of a displaceable valve member on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. Furthermore, an arrangement will hereinafter be called central if it is intended for all the cylinders in common, and local if it is intended for only a single cylinder.
In the pressure-controlled fuel injection system known from EP 0 711 914 A1, with the aid of a high-pressure pump, fuel is compressed to a first, high fuel pressure of approximately 1200 bar and stored in a first pressure reservoir. The fuel at high pressure is also fed into a second pressure reservoir, in which a second high fuel pressure of about 400 bar is maintained by regulating the fuel delivery to the second pressure reservoir by means of a 2/2-way valve. Via a valve control unit, either the lower or the higher fuel pressure is introduced into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from the valve seat by the pressure, so that fuel can emerge from the nozzle opening.
A disadvantage of this known fuel injection system is that first all the fuel has to be compressed to the higher pressure level before some of the fuel can then be relieved to a lower pressure level and stored in a further pressure reservoir. Furthermore, two pressure reservoirs are required in order to store the two fuel pressures.
From International Patent Disclosure WO98/09068, a stroke-controlled injection system is also known, in which again two pressure reservoirs for storing the two fuel pressures are provided. For each pressure reservoir, its own high-pressure pump is provided, which is constantly in operation, specifically including whenever the desired pressure has already built up in the applicable pressure reservoir.
To improve the injection performance and the efficiency, according to the invention, the injection method of the fuel injection systems are set forth. Refinements according to the invention are recited in the disclosure hereinafter.
According to the invention, it is proposed that a lower pressure level be generated during the applicable injection cycle, for instance by means of a local diversion unit or a piezoelectric valve unit. Since these units are independent of the camshaft, they could be in a targeted way as needed. Losses from friction can also be reduced by means of a pressure step-up means that is not permanently in operation.
Further advantages and advantageous refinements of the subject of the invention can be learned from the description, drawing and claims.
Various exemplary embodiments of fuel injection systems according to the invention with a central distributor device, in which fuel is injected at two different high fuel pressures are shown schematically in the drawing and described in further detail below.